A crucible is a utensil or a melting tank made of an extremely refractory material, such as clay, graphite, porcelain clay, quartz or infusible metallic iron. The crucible is generally a ceramic deep-bottom bowl-like container. A crucible is often used when solid objects need to be heated over heavy fire, as it can bear a higher temperature compared with glassware. During the use of a crucible, a crucible cover is generally obliquely placed on the crucible to prevent the heated substance from splashing and allow air to freely get in and out for possible oxidation reactions. The crucible is generally held on a pipeclay triangle for direct heating over fire due to its small bottom. The crucible may be placed on the pipeclay triangle vertically or obliquely, according to experimental needs. The heated crucible can not be immediately put on a cold metal desktop, in case it would be broken due to drastic cooling.
FIG. 1 shows a zinc furnace with a crucible in the prior art. The zinc furnace includes a furnace body 1. A hearth 2 is arranged in the furnace body 1, and a furnace pot 6 is arranged on the upper part of the furnace body 1. Furthermore, an electric furnace plate 3 is arranged at the bottom of the hearth 2, while a heating wire 4 is arranged in the inner cavity of the hearth 2. With reference to FIG. 1, the lower part of a crucible 5 in the hearth 2 is in contact with the heating wire 4, while the upper part of the crucible 5 is located at the bottom of the furnace pot 6. A heat preservation layer 7 is arranged in the furnace body 1 outside the hearth 2. A thermocouple 8 penetrates through the heat preservation layer 7 and the wall of the hearth 2 with one end located in the hearth 2 and the other connected with a control cabinet 9.
When heated with the cubicle, a material could be evaporated till being completely consumed, and the total quantity of the material is determined by the volume of the crucible. However, the crucible heating apparatus used in the prior art generally adopts an integral heating system, wherein the temperature difference over the crucible stays constant. In this case, the bigger the crucible is, or the longer its longitudinal length is, the more difficult it is to control the temperature difference. Meanwhile, when used for evaporation, the crucible leads to certain defects, such as non-uniform melting along the radius of the crucible, rate instability caused by a sudden boiling associated with the length of the crucible, material pyrolysis caused by slow heat conduction inside the material, etc.
Accordingly, although related heating apparatuses and methods in the prior art are able to monitor the temperature in the furnace, i.e. the crucible, through a monitoring element and adjust the temperature through an external controller, the temperature control device, which is relatively simple, can only roughly adjust the temperature in the crucible on the whole, leaving the problems of non-uniform heat transfer and thus non-uniform temperature distribution unsolved. Moreover, as the temperature control device in the prior art controls the temperature in the crucible on the whole, the temperature of each zone of the whole crucible can not be controlled exactly. Local temperature abnormities due to the limited number of sampling points may lead to misjudgment of the temperature control device, thus causing heating failure and even dangerous accidents.